The multi antenna-based wireless communication system uses technologies such as the closed-loop precoding transmission scheme, the Adaptive Modulation and Coding (AMC) scheme, the channel-sensitive scheduling scheme, etc.
Using the closed-loop precoding transmission scheme, a gain of a reception signal may be improved by controlling phases of multi antenna channels. Using the AMC scheme, a transmitter can adjust an amount of transmitted data according to a channel state. Using the channel-sensitive scheduling-based resource management method, the transmitter can selectively provide a service to a user having a good channel state among several users, thus increasing the system capacity as compared with a method of allocating a channel to a user and servicing the user through the allocated channel.
For example, the closed-loop precoding transmission scheme, the AMC scheme, and the channel-sensitive scheduling scheme receive channel information from a receiver and apply proper precoding, modulation, and encoding at the most efficient time point.
In a wireless communication system using the Orthogonal Frequency Division Multiple Access (OFDMA) scheme, one of various reasons for increasing the capacity in the OFDMA scheme is ability to perform the scheduling on an axis of the frequency. Although a capacity gain is acquired according to the time-varying channel characteristic using the channel-sensitive scheduling scheme, it is possible to obtain a higher capacity gain with use of the frequency-varying channel characteristic.
The closed-loop precoding transmission scheme, the AMC scheme, and the channel-sensitive scheduling scheme can improve transmission efficiency if the transmitter acquires sufficient information on a transmission channel. When the transmitter cannot estimate a state of the transmission channel from a reception channel as in the Frequency Division Duplex (FDD) scheme, a receiver reports information on the transmission channel to the transmitter. However, in a wireless communication system environment, a channel state varies over time. Thus, when the report on the channel state is delayed, the efficiencies of the closed-loop precoding transmission scheme, the AMC scheme, and the channel-sensitive scheduling scheme may deteriorate.
In the wireless communication system, one base station (e.g., eNB) is in charge of users within a predetermined coverage area, and when the users move outside of the coverage area, the users are handed over to another base station (e.g., eNB) for maintaining a call.
In the wireless communication system, since a user suffers interference from a signal transmitted from another base station, the channel state of the user is relatively poor. Thus, a user who is located closer to the base station can receive a service with a higher transmission rate, and a user who is located at the boundary of a cell coverage area receives a service with a lower transmission rate. In order to solve the above-mentioned problem, cooperative transmission is expected to be introduced in the 4th generation mobile communication system. The cooperative transmission is a technology for transmitting a signal for a user located at a boundary of a cell.